This invention relates generally to the displaying of three-dimensional medical image, and more particularly to displaying discrete images of objects having the same physical property.
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X-ray computerized axial tomography (CT) produces exact cross-sectional image data that express the physical property (electron density) of the human body. Reconstructions of three-dimensional images using multiple axial images acquired at different axial positions have been performed for some time. Helical-scan X-ray CT scanners and cone-beam X-ray CT scanners have been put to practical use recently. This has enabled more precise three-dimensional image reconstructions.
For three-dimensional display of medical images, a surface rendering method is often used that displays the interfaces between objects after extracting these interface planes from objects constituting a subject, and a volume rendering method is used that is based on a three-dimensional array of voxels having values relating to a physical property of the study subject.
In the case of the volume rendering method, anatomical regions of the subject are classified based on CT values in the three-dimensional array of the voxels that is constructed from X-ray CT slices. Therefore, one can separate spatial regions with different CT values as different objects. A spatial region with the same CT value is classified as one object, so one cannot separate a spatial region with this same CT value into different objects, even if the spatial region with this same CT value is separated geometrically. However, it is often desirable to separate a spatial region with the same CT value into two or more objects.
For example, one may want to remove the front portion of an organ to observe the inside of it so there is a need to separate the spatial region with the same CT value into two or more objects. For example, one may want to remove muscles of a front portion of extremities to observe relations of bones and muscles in these extremities so there is a need to separate the spatial region with the CT value for muscle into two or more objects.
For example, in a case of simulating joint motion, there is a need to separate a spatial region with the same CT value into two or more bones. For example, in the case of simulating a brain operation, there is a need to remove a small part of the skull with the same CT value as the rest of the skull, to open an aperture in the skull and observe inside.
When using the conventional volume rendering method, objects with different CT values can be separated from each other, but objects with same CT value cannot be separated into more than one object, even if the locations of the parts are different.
Volume rendering alone is therefore not suitable for an application that separates the spatial region with the same physical property into two or more objects, such as the simulation of an operation.
Additionally, the conventional volume rendering method requires a large amount of processing power, and reducing the processing time is very important. Therefore, because the processing time increases with the increase in the number of objects rendered, the amount of processing time required to handle a large number of objects means the conventional volume rendering method is often unsatisfactory for practical use.
Furthermore, the conventional volume rendering method permits objects with different physical properties to be separated from each other, but objects with the same physical property cannot be separated into more than one object, even if the locations of the parts are different.
There is a need to subdivide a spatial region with the same physical property into two or more objects while also reducing the processing time required to reconstruct the objects. Furthermore, there is a need to keep processing time at a minimal even if the number of objects is increased.
Multiple objects having the same physical property within a subject are displayed as distinct three-dimensional images in one or more views. Projection data obtained by scanning the subject with electromagnetic radiation are used to create a spatial distribution of absorption values for the subject that is displayed as an image on an image display unit. The spatial distribution is also stored as a series of voxels representing a three-dimensional image of the subject. Particular spatial regions within the image are defined as objects, with each object comprising a set of voxels. The objects are grouped into one or more views using a set selection panel on the image display unit. A density, gradient and color for each object in a view are determined based on properties input through the a series of object property setting panels on the image display unit. Each object in a particular view is associated with one of the property setting panels. A relationship between degrees of opacity and values for the voxels in an object is defined in the property setting panel for the object and used to determine the density. The density, gradient and color for the objects in a view are stored as a parameter set in memory and optionally, on a non-volatile medium for subsequent retrieval. A volume rendering process applies the data in the parameter sets to the stored voxels to create one or more views of the three-dimensional image. A viewpoint parameter provides a common viewpoint for displaying multiple views simultaneously in different areas of a display.
In another aspect of the invention, multiple sets of three-dimensional voxel data are acquired at different times or from different modalities. The parameter sets for one or more views having the same viewpoint are applied to the multiple sets of voxel data. The results can be displayed simultaneously in multiple areas of the display to enable comparisons of images of the objects at different times or with different types of apparatus.
Thus, a spatial region having a uniform physical property within a three-dimensional medical image can be subdivided into two or more objects that are displayed with different colors and opacities. When the number of objects increases, the volume rendering process can build the three-dimensional image quickly because all the necessary information is accumulated in the memory. Since volume rendering requires setting up a number of parameters, the invention can easily perform comparisons of a plurality of views of a three-dimensional image with different parameter settings by applying predefined object parameter-sets to the voxel values of the three-dimensional voxel data, thus eliminating the complicated and troublesome parameter setting process and more accurately reproducing the three-dimensional image.
Therefore, the invention can save processing power and produce a final image in a short processing time. Even if there are two or more objects, it is possible to display them on a single display screen, and it is possible to grasp the spatial relations of two or more objects correctly and easily. Furthermore, by grouping the objects constituting the subject into several views, the invention allows the display of a plurality of objects in multiple views with a common viewpoint.
In addition to the aspects and advantages of the present invention described in this summary, further aspects and advantages of the invention will become apparent by reference to the drawings and by reading the detailed description that follows.